This invention relates to refractors and more particularly to an improved cross-cylinder mechanism.
Refractors are well-known ophthalmic instruments used for determining the proper lens values necessary to correct the defective vision of the patient. The refractor typically includes a right eye battery and a left eye battery, each enabling the practitioner to place various corrective lenses in alignment with one of the patient's eyes. Each of the batteries is alike and each includes a sphere lens assembly and a cylinder lens assembly, with each assembly including a plurality of progressively powered lenses. The practitioner may thereby select specific lenses and place them in alignment with the patient's eye to determine the proper lens values for correcting the patient's vision.
A cross-cylinder assembly is usually used for performing the Jackson cross-cylinder test to determine the accuracy of cylinder power and axis that has been selected for visual correction. The cross-cylinder assembly is usually a lens having plus and minus cylinders of equal power with their cylinder axes 90.degree. apart. This lens is conventionally mounted in a loop which may be selectively "flipped" about a rotational axis that is perpendicular to the patient's visual (test) axis and the rotational axis is spaced midway (45.degree.) between the plus and minus cylinder axes. When the cross-cylinder lens is flipped, the plus and minus cylinder axes exchange places. The prior art further teaches the desirability of mechanically coupling the cross-cylinder assembly to the cylinder lenses of the test battery in order that the flip axis of the cross-cylinder assembly maintains its orientation to the cylinder axis of the correcting cylinder lenses at all times. The rotational axis of the cross-cylinder assembly or flip axis, is aligned parallel to the cylinder axis of the correcting lenses when testing for the accuracy of the selected astigmatic axis. When testing for the accuracy of the power of the selected cylinder lenses, the flip axis of the cross-cylinder assembly is oriented 45.degree. to the correcting cylinder lens axis.
U.S. Pat. No. 3,498,699, issued May 3, 1970 to Wilkinson, discloses a cross-cylinder loop assembly mechanically coupled to correcting cylinder lenses in order to maintain proper orientation of the cross-cylinder assembly and which may be moved from a position along the patient's test axis to a position away from the patient's test axis. The Cross-cylinder assembly is manually flipped along a rotational axis perpendicular to the patient's test axis to conduct the Jackson cross-cylinder tests.
U.S. Pat. No. 3,698,799 issued Oct. 17, 1972 to Pitchford, relates to a refractor having a flip cross-cylinder assembly capable of being "flipped" from a position convenient to the control used to select the correcting cylinder lens axis. Similar to Wilkinson, the device is designed to swing the cross-cylinder assembly in line with or away from the patient's test axis. Likewise, the cross-cylinder lens is flipped to conduct the tests.
U.S. Pat. No. 3,860,330, issued Jan. 14, 1975 to Staffan B. Persson, describes a mechanism for synchronizing the axial orientation of a cross-cylinder lens assembly with the cylinder axis of a correcting cylinder lens. Similar to the preceding patents described above, Persson teaches that the cross-cylinder assembly is pivotably mounted so that it can be swung from a position in alignment with the test axis to a position away from the test axis. Persson also teaches a mechanism for remotely flipping the cross-cylinder lens.